The present invention relates to lactic acid processing. It particularly concerns: methods for separating lactic acid streams and lactate salt streams from mixtures such as fermentation broths; isolating and processing the lactic acid; and, isolating the lactate salt in preferred forms.
The potential of lactic acid as a commodity chemical, for example for use in the production of various industrial polymers, is known. This has been described, for example, in U.S. Pat. Nos.: 5,142,023; 5,247,058; 5,258,488; 5,357,035; 5,338,822; 5,446,123; 5,539,081; 5,525,706; 5,475,080; 5,359,026; 5,484,881; 5,585,191; 5,536,807; 5,247,059; 5,274,073; 5,510,526; and 5,594,095. (The complete disclosures of these seventeen patents, which are owned by the assignee of the present application, Cargill, Inc. of Minneapolis, Minn., are incorporated herein by reference.) There has been general interest in developing improved techniques for generation and isolation of lactic acid. Also, because of their potential commercial value, there is great interest in isolation of the other valuable related lactate products such as lactide, lactate esters and amides, and oligomers; see e.g. the same 17 patents.
In general, large amounts of lactic acid can be readily generated by the conduct of large-scale, industrial, bacterially-conducted fermentation processes, particularly using carbohydrates, such as dextrose, as the feed stock, along with suitable mineral and amino acid based nutrients. Typically, such productions occur at broth temperatures of at least 45xc2x0 C., usually around 48xc2x0 C.
Issues of concern with respect to lactic acid generation include, inter alia, appropriate control of pH within the fermentation system to ensure proper environment for bacterial action; separation and isolation of either or both of lactic acid and lactate salts from the fermentation process; and downstream isolation and production involving the isolated lactic acid or lactic acid derived product.
According to the present disclosure, techniques for processing mixtures of lactic acid and dissolved lactate salts are provided. The preferred techniques are provided for processing fermentation broths, preferably fermentation broths produced with or adjusted to have a pH of less than about 4.8, typically and preferably less than about 4.5, more preferably less than 4.3 and most preferably within the range of about 3.0 to 4.2 inclusive.
The techniques concern processing the mixtures into: (a) a lactic acid stream, component or phase; and, (b) a lactate salt stream component or phase. Preferred techniques are provided so that the lactic acid stream, component or phase can be readily taken on to produce desirable lactate products, such as lactate oligomers, lactide lactate esters, lactate amides and/or polylactate. The preferred processing also provides the lactate salt in a form suitable for further use, such as recycling to a fermentation broth; or, for as a fertilizer or feed.